A mysterious sound heard booming from deep under the ocean waves has finally been traced to a fascinating source. First recorded in 2014 in the west Pacific, the "biotwang" is actually the call of the Bryde's whale (Balaenoptera brydei) traveling long distances in the open ocean. What's more, the techniques used to identify the sound have led to the development of a new tool for understanding whale populations and how they move about in and inhabit Earth's enigmatic seas. "Bryde's whales occur worldwide in tropical and warm temperate waters, but their population structure and movements are not well understood," writes...